<!DOCTYPE html>
<html lang="en">

<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="ie=edge">
	<title>Document</title>
	<script src="./vuev2.5.21.js"></script>
</head>

<body>
	<div id="app">
		<input type="text" v-model="n1">
		<select name="" id="" v-model="opt">
			<option selected value="+">+</option>
			<option value="-">-</option>
			<option value="*">*</option>
			<option value="/">/</option>
		</select>
		<input type="text" v-model="n2">
		<input type="button" value="=" @click="result">
		<input type="text" v-model="n3" readonly>
	</div>
	<script>
		new Vue({
			el: "#app",
			data: {
				n1: 0,
				n2: 0,
				n3: 0,
				opt: "+"
			},
			methods: {
				result() {
					switch (this.opt) {
						case "+":
							this.n3 = parseInt(this.n1) + parseInt(this.n2)
							break
						case "-":
							this.n3 = parseInt(this.n1) - parseInt(this.n2)
							break
						case "*":
							this.n3 = parseInt(this.n1) * parseInt(this.n2)
							break
						case "/":
							this.n3 = parseInt(this.n1) / parseInt(this.n2)
							break
					}

				}
			}
		})
	</script>
</body>

</html>